1. Field of the Invention
The present invention is directed to the field of removing harmful and waste materials having low heat content, particularly refuse, by means of combustion utilizing a cementmaking plant as the source of heat and binder materials.
2. Description of the Prior Art
Harmful and waste materials such as household wastes, community wastes, agricultural wastes and industrial refuse invariably contain some combustible substances. Nearly all known methods for the removal of such refuse have serious disadvantages which have never heretofore been eliminated.
For example, in refuse composting, heavy metal compounds capable of being leached reach the biological cycle and accumulate. In some cases, there are also found harmful organic compounds and/or harmful bacteria, salmonella and other pathogenic bacteria in the compost.
Similar dangers of contamination of ground and ground water exist with a deposit of refuse. Through leaching or decomposition, such deposits can yield harmful substances, poisons, and the like which enter into the ground and ground water. Beyond this, in heavily populated areas, depositing places are not readily available, and constitute a source of annoyance for the population, and are not usable as building ground or utilitarian land even decades after the deposit has been closed up.
The removal of harmful and waste substances such as refuse accordingly constitutes a complicated problem. This holds true particularly if the waste materials are removed by means of combustion. When such materials are burned, harmful substances adversely affecting the environment are released, such, for example, as nitric oxide, compounds of sulphur, halogens, or alkalies, as well as vapors from heavy metals. Also, in many cases, the heat content of the combustible portions or exhaust gases is not utilized and is lost.
Community household refuse in many cases has to be treated in expensive refuse combustion installations. Such refuse contains, for example, combustible portions with an average heating value of 2000 to 2200 kcal/kg. Refuse combustion installations which at one time seemed to provide the answer for the refuse problem have in recent times been criticized because of their emission of harmful substances into flue gas and the production of leaching prone heavy metal residues in the flue dust or the wash water. Some of these installations therefore had to be left standing idle. In the case of ordinary grate fires in refuse combustion installations with combustion air temperatures in the area of 400 to 500.degree. C., the firing does not reach the temperatures necessary for the reliable reduction of organic toxic compounds such as dioxin or polychlorinated diphenyl. Also, the heavy metals reaching the flue dust or the wash water are not in a leaching resistant form and accumulate to dangerous concentrations upon their deposit. Added to this is the disadvantage, in addition to the increased cost, that there is a difficulty of maintaining the combustion temperature on the grate substantially constant.
Even the pyrolysis of refuse which at one time appeared promising, brings appreciable problems. The limitation of capacity of the distillation chambers is a disadvantage. A distillation process with an air cut-off and heat supply can apparently take place solely in closed chambers in a discontinuous manner. In this connection, danger to the environment exists if, through carelessness in the conduction of the process, the vaporization temperatures exceed or fall below certain limits. In this case, the formation of dioxins through pyrolysis of chlorine-containing scraps of synthetic material is likely to occur. Just as in the case of the grate firing, the process of pyrolysis is also subject to appreciable difficulties and risks.